1. Field of the Invention
The invention relates to a method for determining the rotational speed of a part among a plurality of components included in a torsional vibration prone system and coupled with respect to their rotatability. The invention furthermore relates to a method for determining the slippage of a continuously variable transmission (CVT) and a method for controlling a CVT. Additionally the invention relates to a belt-driven conical-pulley transmission.
2. Description of the Related Art
Transmissions with continuously variable gear ratios, so-called continuously variable transmissions (CVT) (for example belt-driven conical-pulley transmissions, friction gear transmissions, etc), are increasingly being used in motor vehicles for reasons of comfort and reduced fuel consumption, which are actuated such by a control unit that depending on the activation of a gas pedal or a request that can be input by the driver on one hand, a satisfactory dynamic vehicle behavior results, and on the other hand driving occurs with low fuel consumption. FIG. 1 shows an example of a motor vehicle power train.
A motor vehicle has an engine 2, which in the illustrated example is connected to a cardan shaft 8 by means of a clutch 4 and a transmission 6. By means of a differential 10, the cardan shaft drives the drive shafts 12, which are non-rotatably connected to rear wheels 14. The front wheels 16 are also shown in the illustrated example.
An electronic control unit 18 with a microprocessor and corresponding storage devices has inputs 20 that are connected to sensors. A sensor 22 for detecting the rotational speed of a transmission input shaft, a throttle valve sensor 24, an engine speed sensor 26, a wheel rotational speed sensor 28, for example, and possibly further sensors are provided. Outputs of the control unit 18 are connected to a clutch-activating device 32 and a transmission-activating device 34, as well as possibly with additional actuators of the power train, such as a throttle valve regulating unit, etc.
The transmission 6 is a CVT in the example represented, the activating device 34 of which is selected hydraulically. By means of a selector lever 36 a reverse travel step as well as several shifting programs can be activated.
Various problems arise in the practical operation of such power trains equipped with continuously variable transmissions, the solution of which is important for a comfortable and also reliable use of the CVT over extended operating periods. It is important, for example, for the control or regulation unit of the CVT to know the exact rotational speed of its input shaft. The ability to use an input rotational speed signal detected directly on the input shaft for control or regulating purposes, of for example the transmission ratio of the CVT, is limited since the input rotational speed can have oscillations that are present in the power train. Moreover it is required for various reasons to detect slippage of the CVT operating with frictional engagement to avert permanent damage. The gear ratio change is also subject to problems, especially in the case of belt-driven conical-pulley transmissions whose conical pulley pairs each have only one pressure chamber for pressing and adjustment.
The invention is based upon the objective of providing remedies for the aforementioned problems occurring in practice.